Frames crash multi-measure rests

Steps to reproduce bug
1. Open a score that contains horizontal frames (such as Ode-2949.mscz )
2. Style > Edit General Style
3. Mark "Create multi-measure rests"
4. Press OK

--> Crash

MuseScore version: r. 2955 nightly

(Operating System: Windows 7)

first reported by ritmus: http://musescore.org/fr/node/5305